Long-wave athermalization optical imaging lens

Abstract

The invention provides a long-wave athermalization optical imaging lens. The long-wave athermalization optical imaging lens comprises a first lens, a second lens, a third lens, a fourth lens and a fifth lens which are sequentially arranged on an optical path from an object side to an image side, a second lens which is a biconcave lens having a negative refractive power; the third lens is a meniscus lens with positive focal power; the fourth lens is a meniscus lens with negative focal power; the first lens, the second lens, the third lens and the fourth lens are made of at least three lens materials. The lens material comprises chalcogenide glass, a ZnS crystal and a germanium crystal. According to the invention, thermal difference and chromatic aberration of an optical system are eliminated through the combination of different lens materials and the surface design of the aspherical mirror, so that the optical imaging lens can perform clear imaging without refocusing under the conditions that the working spectrum is 8-12 [mu] m and the working temperature is-40 DEG C to 60 DEG C; the system is suitable for the fields of security, unmanned aerial vehicles, industrial monitoring, temperature measurement, forest fire prevention and the like.

Description

Technical Field

[0001] The present invention relates to the field of optical imaging information technology, and in particular to a long-wave athermal optical imaging lens. Background Art

[0002] Infrared imaging is based on the difference in radiation between the target and the background. According to Planck's blackbody radiation law, long-wave infrared with a wavelength of 8 to 12 μm is used to detect the contours of objects at normal temperature.

[0003] There are three main methods for athermalization of infrared optical systems: mechanical passive, electromechanical active, and optical passive. Although mechanical passive and electromechanical active are easy to implement, they only compensate for image displacement and cannot guarantee focal length compensation. Moreover, due to the use of mechanical devices, the system is inevitably complicated, the volume becomes larger, the weight increases, and the reliability decreases. Optical passive athermalization technology not only guarantees the focal length compensation of the system, but also has the advantages of relatively simple structure, small size, light weight, and high system reliability. It has been widely used in the design of athermalization of infrared optical systems.

[0004] However, infrared optical materials are sensitive to ambient temperature. As the ambient temperature changes, the focal length, image plane position and aberration of the infrared optical system will change, resulting in a decrease in imaging quality. Summary of the invention

[0005] The purpose of the present invention is to provide a long-wave athermal optical imaging lens that can solve at least one of the above-mentioned technical problems. The specific solution is as follows:

[0006] According to a specific embodiment disclosed in the present invention, the present invention discloses a long-wave athermal optical imaging lens, comprising:

[0007] The following are set in order on the optical path from the object side to the image side:

[0008] A first lens, wherein the first lens is a meniscus lens with positive optical power;

[0009] A second lens, wherein the second lens is a biconcave lens with negative optical power;

[0010] A third lens, wherein the third lens is a meniscus lens with positive optical power;

[0011] a fourth lens, wherein the fourth lens is a meniscus lens with negative optical power;

[0012] Wherein, the lens materials of the first lens, the second lens, the third lens and the fourth lens are

[0013] There are at least three types of materials;

[0014] The lens materials include: chalcogenide glass, ZnS crystal and germanium crystal.

[0015] Preferably, the lens material of the first lens and the fourth lens is chalcogenide glass;

[0016] The lens material of the second lens is ZnS crystal;

[0017] The lens material of the third lens is germanium crystal.

[0018] Preferably, the image side surface of the second lens, the image side surface of the third lens and the image side surface of the fourth lens are all aspherical surfaces.

[0019] Preferably, the aspheric surface shapes of the second lens, the third lens and the fourth lens satisfy the expression:

[0020]

[0021] Where c is the curvature at the vertex, and r is the radial coordinate length;

[0022] k is the coefficient of the quadratic curve;

[0023] a, a2, a3, and a4 are the coefficients of higher-order terms respectively.

[0024] Preferably, in the surface shape expression of the aspheric surface of the second lens: k=4.634,

[0025] a=4.689×10 -7 , a2=4.898×10 -11 , a3=8.560×10 -13 , a4=2.056×10 -15 ;

[0026] In the aspheric surface expression of the third lens: k = -0.257,

[0027] a=2.163×10 -6 , a2=1.235×10 -8 , a3=6.503×10 -12 , a4=2.969×10 -15 ;

[0028] In the aspheric surface expression of the fourth lens: k = -4.621,

[0029] a=1.762×10 -5 , a2=1.373×10 -9 , a3=8.675×10 -10 , a4=3.919×10 -12 .

[0030] Preferably, the center thickness of the first lens is 10.8 mm;

[0031] The center thickness of the second lens is 8.0 mm;

[0032] The central thickness of the third lens is 8.6 mm;

[0033] The central thickness of the fourth lens is 10.0 mm.

[0034] Preferably, the grade of the chalcogenide glass is HWS6.

[0035] Preferably, the focal length of the first lens and the focal length of the near-infrared optical imaging lens satisfy the following relationship: 1.3 <f1 / f<1.8;

[0036] The focal length of the second lens and the focal length of the near-infrared optical imaging lens satisfy: -4.7 <f2 / f<-3.8;

[0038] The focal length of the third lens and the focal length of the near-infrared optical imaging lens satisfy: 0.8 <f3 / f<1.5;

[0039] The focal length of the fourth lens and the focal length of the near-infrared optical imaging lens satisfy: 8.3 <f4 / f<13.4。

[0040] Preferably, it also includes: a parallel plate;

[0041] The air gap between the second lens and the first lens is: 25.4mm;

[0042] The air gap between the third lens and the second lens is: 27.2mm;

[0043] The air gap between the fourth lens and the third lens is: 6.0 mm;

[0044] The air gap between the parallel flat plate and the fourth lens is 5.7 mm.

[0045] Preferably, the focal length of the optical imaging lens is 60 mm, the F / # is 1, the operating band is 8-12 μm, and the operating temperature is -40°C-60°C.

[0046] Compared with the prior art, the above solution of the embodiment disclosed in the present invention has at least the following beneficial effects:

[0047] The present invention eliminates thermal differences and chromatic aberrations of the optical system through a combination of different lens materials and a surface design of an aspherical mirror, so that the optical imaging lens can produce clear images without refocusing under the conditions of an operating spectrum of 8-12 μm and an operating temperature of -40°C to 60°C. The present invention is suitable for applications in security, drones, industrial monitoring, temperature measurement, forest fire prevention and other fields. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] The drawings herein are incorporated into the specification and constitute a part of the specification, showing embodiments consistent with the disclosure of the present invention, and together with the specification, are used to explain the principles disclosed in the present invention. Obviously, the drawings described below are only some embodiments disclosed in the present invention, and for ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work. In the drawings:

[0049] Figure 1 A schematic diagram of the structure of an optical imaging lens provided by an embodiment of the present invention;

[0050] Figure 2 This is an MTF curve diagram of an embodiment of the present invention at -40°C;

[0051] Figure 3 This is an MTF curve diagram of an embodiment of the present invention at -20°C;

[0052] Figure 4 This is an MTF curve diagram of an embodiment of the present invention at 0°C;

[0053] Figure 5 This is an MTF curve diagram of an embodiment of the present invention at 20°C;

[0054] Figure 6 This is an MTF curve diagram of an embodiment of the present invention at 40°C;

[0055] Figure 7 This is an MTF curve diagram of an embodiment of the present invention at 60°C;

[0056] Figure 8 Graph showing an optical field curvature-distortion curve according to an embodiment of the present invention.

[0057] Reference numerals:

[0058] L1, first lens; S1, object side surface of the first lens; S2, image side surface of the first lens;

[0059] L2, second lens; S3, object-side surface of the second lens; S4, image-side surface of the second lens;

[0060] L3, the third lens; S5, the object side surface of the third lens; S6, the image side surface of the third lens;

[0061] L4, the fourth lens; S7, the object-side surface of the fourth lens; S8, the image-side surface of the fourth lens;

[0062] L5, parallel plate; S9, incident surface of the parallel plate; S10, exit surface of the parallel plate;

[0063] S11, detection surface. DETAILED DESCRIPTION

[0064] In order to make the purpose, technical solution and advantages of the present invention more clear, a long-wave athermal optical imaging lens disclosed in the present invention will be further described in detail below in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments disclosed in the present invention, rather than all the embodiments. Based on the embodiments disclosed in the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection disclosed in the present invention.

[0065] It should also be noted that the terms "include", "comprises" or any other variations thereof are intended to cover non-exclusive inclusion, so that a product or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such product or device. In the absence of more restrictions, the elements defined by the sentence "comprises a" do not exclude the presence of other identical elements in the product or device including the elements.

[0066] In the drawings, the thickness, size and shape of the lenses have been slightly exaggerated for ease of illustration. Specifically, the shapes of the spherical or aspherical surfaces shown in the drawings are shown by way of example. That is, the shapes of the spherical or aspherical surfaces are not limited to the shapes of the spherical or aspherical surfaces shown in the drawings. The drawings are for illustration only and are not drawn strictly to scale.

[0067] The following is combined with Figure 1-8 Alternative embodiments of the present invention are described in detail.

[0068] In this embodiment, the surface of each lens close to the detection surface S11 is the image side surface of the lens, and the surface of each lens close to the object side is the object side surface of the lens. If the object side surface of the lens is far away from the detection surface, the object side surface of the lens is convex; otherwise, the object side surface is concave. If the image side surface of the lens is far away from the detection surface, the image side surface of the lens is concave; otherwise, the image side surface is convex.

[0069] like Figure 1As shown, according to a specific embodiment of the present invention, the present invention provides a long-wave athermal optical imaging lens, comprising: a first lens L1, a second lens L2, a third lens L3, an aperture S7, a fourth lens L4, a fifth lens L5 and a parallel plate arranged in sequence on an optical path from the object side to the image side.

[0070] Specifically, the first lens L1 is a meniscus lens with positive focal power; the second lens L2 is a biconcave lens with negative focal power; the third lens L3 is a meniscus lens with positive focal power; and the fourth lens L4 is a meniscus lens with negative focal power. The focal length of the optical imaging lens is 60mm, the F / # is 1, the operating band is 8-12μm, and the operating temperature is -40℃-60℃.

[0071] Furthermore, the first lens L1, the second lens L2, the third lens L3 and the fourth lens L4 are made of at least three types of lens materials, including: chalcogenide glass, ZnS crystal and germanium crystal.

[0072] Preferably, the grade of the chalcogenide glass is HWS6.

[0073] In this embodiment, chalcogenide glass having high transmittance and small refractive index temperature coefficient in the long-wave infrared band (8-12 μm) and infrared crystal materials with high Abbe numbers and small Abbe numbers such as ZnS and germanium are combined to eliminate thermal differences and chromatic aberrations.

[0074] Preferably, the material of the first lens L1 and the fourth lens L4 is HWS6;

[0075] The material of the second lens L2 is ZnS crystal, and the material of the third lens L3 is germanium crystal.

[0076] The present invention eliminates the thermal difference of the optical system by combining different lens materials, so that the optical imaging lens can form a clear image without refocusing under the conditions of a working spectrum of 8-12 μm and a working temperature of -40°C to 60°C.

[0077] In this embodiment, the image side surface S4 of the second lens, the image side surface S6 of the third lens, and the image side surface S8 of the fourth lens are all aspherical surfaces, and the aspherical surfaces are used to reduce the monochromatic aberration of the optical system.

[0078] Specifically, the aspheric surface uses an even-order aspheric surface. The shape of the aspheric surface cannot be defined only by curvature, but also requires other parameters to characterize the degree of deviation from the reference spherical surface. The most commonly used even-order aspheric surface in optical design software is defined according to the sagittal height. The expression of the aspheric surface shape is as follows:

[0079]

[0080] Where c is the curvature at the vertex;

[0081] k is the coefficient of the quadratic curve;

[0082] a, a2, a3, and a4 are the coefficients of higher-order terms respectively.

[0083] In a preferred embodiment of the present invention,

[0084] The parameters in the surface expression of the image side surface S4 of the second lens are as follows: k = 4.634,

[0085] a=4.689×10 -7 , a2=4.898×10 -11 , a3=8.560×10 -13 , a4=2.056×10 -15 .

[0086] The parameters in the surface shape expression of the image side surface S6 of the third lens are as follows: k = -0.257,

[0087] a=2.163×10 -6 , a2=1.235×10 -8 , a3=6.503×10 -12 , a4=2.969×10 -15 .

[0089] The parameters in the surface shape expression of the image side surface S8 of the fourth lens are as follows: k = -4.621,

[0090] a=1.762×10 -5 , a2=1.373×10 -9 , a3=8.675×10 -10 , a4=3.919×10 -12 .

[0091] Furthermore,

[0092] The center thickness of the first lens is 10.8 mm, the curvature radius of the object side surface S1 of the first lens is 63.94 mm, and the curvature radius of the image side surface S2 of the first lens is 91.00 mm;

[0093] The center thickness of the second lens is 8.0 mm, the radius of curvature of the object side surface S3 of the second lens is -771.03 mm, and the radius of curvature of the image side surface S4 of the second lens is 511.97 mm;

[0094] The central thickness of the third lens is 8.6 mm, the curvature radius of the object side surface S5 of the third lens is 29.84 mm, and the curvature radius of the image side surface S6 of the third lens is 31.74 mm;

[0095] The center thickness of the fourth lens is 10.0 mm, the radius of curvature of the object-side surface S5 of the fourth lens is 68.31 mm, and the radius of curvature of the image-side surface S6 of the fourth lens is 63.01 mm.

[0096] Furthermore,

[0097] The air gap between the second lens and the first lens is 25.4 mm, the air gap between the third lens and the second lens is 27.2 mm, and the air gap between the fourth lens and the third lens is 6.0 mm.

[0098] Furthermore,

[0099] The focal length of the first lens and the focal length f of the near-infrared optical imaging lens satisfy: 1.3 <f1 / f<1.8;

[0100] The focal length of the second lens and the focal length f of the near-infrared optical imaging lens satisfy: -4.7 <f2 / f<-3.8;

[0101] The focal length of the third lens and the focal length f of the near-infrared optical imaging lens satisfy: 0.8 <f3 / f<1.5;

[0102] The focal length of the fourth lens and the focal length f of the near-infrared optical imaging lens satisfy: 8.3 <f4 / f<13.4。

[0103] In a preferred embodiment of the present invention, a parallel flat plate is provided in front of the detection surface S11 as a protective glass.

[0104] The thickness of the parallel plate is 1.0 mm, the air gap between the parallel plate and the fourth lens is 5.7 mm, and the air gap between the parallel plate and the detection surface S11 is 2.1 mm.

[0105] Table 1 shows the parameters of each lens in a preferred embodiment of the present invention.

[0106] Table 1 Lens parameters

[0107]

[0108]

[0109] Figure 2-Figure 7 The MTF test result curves of the long-wave athermal optical imaging lens of the present invention at the working band of 8-12 μm are divided into -40°C, -20°C, 0°C, 20°C, 40°C and 60°C.

[0110] The image quality evaluation standard of the optical design is based on the optical transfer function (MTF) at the Nyquist frequency (@34mm / lp). It can be seen that the image quality of the long-wave athermal optical imaging lens of the present invention is uniform and close to the diffraction limit within the working distance.

[0111] Depend on Figure 8 It can be seen from the figure that the field curvature and distortion of the long-wave athermal optical imaging lens of the present invention are corrected under the corresponding field of view, and the optical distortion is corrected.

[0112] Finally, it should be noted that the various embodiments in this specification are described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the various embodiments can be referred to each other. For the system or device disclosed in the embodiment, since it corresponds to the method disclosed in the embodiment, the description is relatively simple, and the relevant parts can be referred to the method part description.

[0113] The above embodiments are only used to illustrate the technical solutions disclosed in the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, a person skilled in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some of the technical features may be replaced by equivalents. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments disclosed in the present invention.

Claims

1. A long-wave athermal optical imaging lens, characterized in that: Including the following settings in sequence on the optical path from the object side to the image side: A first lens, wherein the first lens is a meniscus lens with positive optical power; A second lens, wherein the second lens is a biconcave lens with negative optical power; A third lens, wherein the third lens is a meniscus lens with positive optical power; a fourth lens, wherein the fourth lens is a meniscus lens with negative optical power; Wherein, the lens materials of the first lens, the second lens, the third lens and the fourth lens are of at least three types; The lens materials include: chalcogenide glass, ZnS crystal and germanium crystal.

2. The optical imaging lens according to claim 1, wherein: The lens material of the first lens and the fourth lens is chalcogenide glass; The lens material of the second lens is ZnS crystal; The lens material of the third lens is germanium crystal.

3. The optical imaging lens according to claim 1, wherein: The image side surface of the second lens, the image side surface of the third lens, and the image side surface of the fourth lens are all aspherical surfaces.

4. The optical imaging lens according to claim 1, wherein: The aspheric surfaces of the second lens, the third lens and the fourth lens satisfy the expression: Where c is the curvature at the vertex, and r is the radial coordinate length; k is the coefficient of the quadratic curve; a, a2, a3, and a4 are the coefficients of higher-order terms respectively.

5. The optical imaging lens according to claim 4, characterized in that: In the aspheric surface expression of the second lens: k = 4.634, <h2 style=";text-align:left;direction:ltr">a = 4.689×10<h2 style=";text-align:left;direction:ltr"> -7 <h2 style=";text-align:left;direction:ltr"> ,a2 = 4.898×10<h2 style=";text-align:left;direction:ltr"> -11 <h2 style=";text-align:left;direction:ltr"> ,a3 = 8.560×10<h2 style=";text-align:left;direction:ltr"> -13 <h2 style=";text-align:left;direction:ltr"> a4 = 2.056×10<h2 style=";text-align:left;direction:ltr"> -15 <h2 style=";text-align:left;direction:ltr"> ; In the aspheric surface expression of the third lens: k = -0.257, <h2 style=";text-align:left;direction:ltr">a = 2.163×10<h2 style=";text-align:left;direction:ltr"> -6 <h2 style=";text-align:left;direction:ltr"> ,a2 = 1.235×10<h2 style=";text-align:left;direction:ltr"> -8 <h2 style=";text-align:left;direction:ltr"> ,a3 = 6.503×10<h2 style=";text-align:left;direction:ltr"> -12 <h2 style=";text-align:left;direction:ltr"> a4 = 2.969×10<h2 style=";text-align:left;direction:ltr"> -15 <h2 style=";text-align:left;direction:ltr"> ; In the aspheric surface expression of the fourth lens: k = -4.621, <h2 style=";text-align:left;direction:ltr">a = 1.762×10<h2 style=";text-align:left;direction:ltr"> -5 <h2 style=";text-align:left;direction:ltr"> ,a2 = 1.373×10<h2 style=";text-align:left;direction:ltr"> -9 <h2 style=";text-align:left;direction:ltr"> ,a3 = 8.675×10<h2 style=";text-align:left;direction:ltr"> -10 <h2 style=";text-align:left;direction:ltr"> a4 = 3.919×10<h2 style=";text-align:left;direction:ltr"> -12 <h2 style=";text-align:left;direction:ltr"> 。 6. The optical imaging lens according to claim 1, wherein: The center thickness of the first lens is 10.8 mm; The center thickness of the second lens is 8.0 mm; The central thickness of the third lens is 8.6 mm; The central thickness of the fourth lens is 10.0 mm.

7. The optical imaging lens according to claim 1, wherein: The grade of the chalcogenide glass is HWS6.

8. The optical imaging lens according to claim 1, wherein: The focal length of the first lens and the focal length of the near-infrared optical imaging lens satisfy: 1.3 <f1 / f<1.8; The focal length of the second lens and the focal length of the near-infrared optical imaging lens satisfy: -4.7 <f2 / f<-3.8; The focal length of the third lens and the focal length of the near-infrared optical imaging lens satisfy: 0.8 <f3 / f<1.5; The focal length of the fourth lens and the focal length of the near-infrared optical imaging lens satisfy: 8.3 <f4 / f<13.4。 9. The optical imaging lens according to claim 1, wherein: Also includes: Parallel plates; The air gap between the second lens and the first lens is: 25.4mm; The air gap between the third lens and the second lens is: 27.2mm; The air gap between the fourth lens and the third lens is: 6.0 mm; The air gap between the parallel flat plate and the fourth lens is 5.7 mm.

10. The optical imaging lens according to any one of claims 1 to 9, characterized in that: The optical imaging lens has a focal length of 60 mm, an F / # of 1, an operating band of 8-12 μm, and an operating temperature of -40°C-60°C.

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